Myocardial remodeling (i.e. commonly known as myocardial hypertrophy) refers that the symptom where cardiocytes are constant in quantity but increase in volume. It is an orchestrated response of cardiocytes to various pathological stimuli and can be resulted from stimulation with hemorheological inducements such as hypertension, valvular heart disease, acute myocardial infarction, congenital heart disease and exercise-induced increase in pressure load as well as humoral endocrine substances such as endothelin, angiotensin II, catecholamines, transforming growth factor β, interleukin-1, thereby having extremely high morbility rate[1]. Only for hypertension alone, the morbility rate is 15-20% in the West. Although the rate is slightly lower in China, the number of patients exceeds 150 million. Myocardial hypertrophy can offer certain compensation at the initial stage of the symptom. As the condition progresses, myocardial hypertrophy can lead to impaired heart function through abnormalities such as disordered myocardial fiber rearrangement and dysfunctioned cardiac contractile and the like, and it may further develop into heart failure. Myocardial hypertrophy is a major mortality contributor as it advances heart failure which in turn causes death. Thus, exploration on a specific drug effective in treating and controlling myocardial hypertrophy is not only the subject matter and research hot-spot facing scientists, but also a major public health concern demanding immediate solution around the globe.
To date, there has been no in-clinic therapeutic drug specific for treating myocardial hypertrophy, mainly due to its multiple etiological causes and complex underlying mechanism. Research studies have shown that the stretch stimulation caused by hemorheological changes or the stimulation by a humoral endocrine substance (being reciprocal causation in disease) can induce pathological responses, such as myocardial hypertrophy, interstitial fibrosis, etc., almost all through the corresponding receptor and post-receptor signal transduction events[2]. Based on such a finding, therapies targeting etiological causes for myocardial hypertrophy were attempted using an endothelin antagonist, a hypotensive drug, an angiotensin convertase inhibitor, etc, which proved to be somewhat effective. However, since many factors and receptors are involved in the pathological response, and additionally, the above-described antagonists/inhibitors can induce up-regulation of their corresponding receptors and the increase in compensatory secretion of ligands to other related receptors while suppress the function of a signal molecule, the treatment effect turns out to be very limited[3-6]. Therefore, there is a great need to develop a specific drug useful in prophylaxis and treatment through more fundamental pathways.
G proteins are heterotrimeric GTP binding proteins consisting of subunit α, β, and γ and play a key role in transduction of stimulatory signals from extracellular space into intracellular space. Norepinephrine (NE), endothelin (ET), angiotensin II (Ang II), and the like agonize an α1-AR, an AT1 receptor, and an endothelin receptor, respectively, then activate the effector enzyme, phospholipase C (PLC-β), through Gq family G proteins, which enzyme in turn acts on PIP2 to produce DAG and IP3; and induce embryonic gene expression within a cell commonly via the signal pathway of DAG-PKC-Ras-MAPK and IP3-Ca2+-CaN/CaMPKII-NFAT3/GATA-4, resulting in myocardial remodeling. In addition to activating Raf1 through integrins, stretch stimuli may stimulate secretion of AngII, NE, and ET1, and thus is also closely related with Gq. Furthermore, It is observed in experiments that: {circle around (1)} during the pathological process of myocardial remodeling, the Gq signal is significantly excessive, level of which is significantly higher than the physiological Gq signal in normal tissues; both the function and the morphology of the cardiocyte is not significantly altered when Gqα expression is increased two-fold (or below), myocardial hypertrophy and the contractile dysfunction in the heart occur when Gqα expression increased four-fold, the heart failure come about when Gqα expression increased eight-fold; {circle around (2)} over-expression of Gqα gene in a transgenic manner in the heart of a mouse may induce the apparent myocardial hypertrophy and the fatal heart failure in the animal; {circle around (3)} knock out of Gqa expression in the heart can significantly attenuate the hypertrophic response of the heart to pressure load[7-9]. Thus, it can be seen that the Gqα plays a central role in occurrence and development of myocardial remodeling, and it is considered as a common target for multiple signal pathways and a key signal element for mediating myocardial remodeling/hypertrophy caused by various factors. Therefore, regulation on Gqα is expected to be a novel strategy and maybe a successful way for reversing myocardial remodeling/hypertrophy.
However, transgenic animals are a class of animals into which the exogenous gene is introduced by experimental means, integrated stably within the chromosomal genome and capable of being inherited to their offspring; the principle for breeding transgenic animals is as follows: a gene/fragment of interest tackled with processes in molecular biology is injected into zygotes/preimplantation embryonic cells of experimental animals by various genetic procedures, the injected zygote/preimplantation embryonic cell is further transplanted into the oviduct or uterus of the recipient animal and allowed to develop into a transgenic animal carrying the exogenous gene, and the function of the exogenous gene is annotated by analyzing the integration status of the exogenous gene in the transgenic animal and the phenotype of the transgenic animal, and those genetically engineered animals with excellent quality are bred by typical genetic breeding method. Thus, based on current technology, treating adult-onset myocardial remodeling/hypertrophy in human with transgenic techniques is neither impractical nor rational. Additionally, knocking out expression of Gqα in the heart will result in severely toxic side effects because Gqα also has important physiological functions. Thus, the two strategies and methods described above have no practical applicable value in clinical management of myocardial remodeling/hypertrophy.
For this reason, we have prepared a series of polypeptides with significant activities for reversing myocardial remodeling/hypertrophy by using systematical techniques, such as, molecule design, optimization, genetic engineering, polypeptide preparation, screening for in vitro and in vivo activities, etc.